Reduce CPU time spent in ingest path about frostdb

[cyriltovena]

FrostDB uses a lot of OpenFile for reading row in memory. I think segmentio/parquet-go#255 will help.

I went for the pool per schema/dynamic columns as I think over allocating is fine as long as you can reuse.

So far this what I have.

❯ benchstat before.txt after.txt
name                                       old time/op    new time/op    delta
_Table_Insert_10Rows_10Iters_10Writers-16     460ms ±14%     586ms ±12%  +27.44%  (p=0.008 n=5+5)

name                                       old alloc/op   new alloc/op   delta
_Table_Insert_10Rows_10Iters_10Writers-16     794MB ±30%     293MB ±59%  -63.15%  (p=0.008 n=5+5)

name                                       old allocs/op  new allocs/op  delta
_Table_Insert_10Rows_10Iters_10Writers-16     1.49M ±52%     0.76M ±24%  -49.11%  (p=0.016 n=5+5)

I'm still playing around though.

[cyriltovena]

That's what I actually do.

[brancz]

Nice! We should also be able to re-use writers and use a sync.Pool on a per schema basis for those as well. I think that will optimize away another fair bit.

[thorfour]

Closing as I believe this has been addressed with many changes, notably the new index.